Methods of cutting bevel gears

ABSTRACT

The present invention comprises novel methods and techniques for the rough cutting of bevel gears, particularly spiral bevel or hypoid pinions, wherein there is contemplated a two-stage roughing operation to be followed by finishing operations. In the preliminary or first stage roughing operation, the tapered tooth slots will only be cut to partial depth, and not to the desired, final roughed depth, and the cutting action will comprise a relative plunge feed between tool and work followed by a cutting generating roll. This generating roll will be abbreviated or of a lesser amplitude than the generating roll that would be required to cut the roughed tooth slot by a generating action alone. In the second stage roughing operation, the tapered tooth slots preferably are roughed out to full or substantially full depth with a full generating roll, and with cutting action taking place on both the forward and return generating rolls, so as to more closely approximate the final, finished tooth shape whereby finishing operations may be facilitated. It is also contemplated that this two-stage roughing operation be performed with cutting going on simultaneously on two workpieces, one at each roughing station, and further be combined with a process utilizing means for automatically loading and unloading the work at the two roughing stations, with the workpieces being automatically transferred from the first to the second roughing station with automatic stock division taking place in that transfer, and with a feeding of the workpieces to a first region where they are to be moved to the first roughing station, and with a discharge region for receiving the final roughed workpieces from the second roughing station for ultimate transfer to a finishing operation.

United States Patent [72] lnventors MeriwetherL.Baxter,Jr.

Pittsiord; Edward Stark, Rochester, both of, N.Y. [2|] Appl. No. 769,187[22! Filed Oct. 21, 1968 [45] Patented June 8,1971 [73] Assignee TheGleason Works Rochester, N.Y.

[54] METHODS OF CUTTING BEVEL GEARS 21 Claims, 20 Drawing Figs.

Primary ExaminerGil Weidenfeld Anorneys-Cushman, Darby and Cushman andMorton A.

Polster ABSTRACT: The present invention comprises novel methods andtechniques for the rough cutting of bevel gears, particularly spiralbevel or hypoid pinions, wherein there is contemplated a twostageroughing operation to be followed by finishing operations. In thepreliminary or first stage roughing operation, the tapered tooth slotswill only be cut to partial depth, and not to the desired, final rougheddepth, and the cutting action will comprise a relative plunge feedbetween tool and work followed by a cutting generating roll. Thisgenerating roll will be abbreviated or of a lesser amplitude than thegenerating roll that would be required to cut the roughed tooth slot bya generating action alone. In the second stage roughing operation, thetapered tooth slots preferably are roughed out to full or substantiallyfull depth with a full generating roll, and with cutting action takingplace on both the forward and return generating rolls, so as to moreclosely approximate the final, finished tooth shape whereby finishingoperations may be facilitated.

It is also contemplated that this two-stage roughing operation beperformed with cutting going on simultaneously on two workpieces, one ateach roughing station, and further be combined with a process utilizingmeans for automatically loading and unloading the work at the tworoughing stations, with the workpieces being automatically transferredfrom the first to the second roughing station with automatic stockdivision taking place in that transfer, and with a feeding of theworkpieces to a first region where they are to be moved to the firstroughing station, and with a discharge region for receiving the finalroughed workpieces from the second roughing station for ultimatetransfer to a finishing operation.

R4770 OF ROLL PATENTEUJUN 8|87| 3583278 SHEET 02 0F 11 MERIWETHERL.BAXTER JR. EDWARD STARK INVENTORS FIG. 3 w 'a PATENTEDJUN 8197i3,583,278

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Mi w w M my V y/ Q Mi a? Z W [e Z 0 QMN QM V \II METHODS OF CUTTINGBEVEL GEARS BACKGROUND AND OBJECTS The present invention relates togear-making, and in particular to methods and techniques for cuttingbevel gears.

The present invention is part of an overall, general development of theGleason Works which includes several inventions besides that disclosedand claimed herein. This development includes other inventions such as anovel structural orientation of cradle, workhead assembly and associatedstructures, by themselves, and in combination with novel control meansfor the generating train, novel cradle housing and cradle assembly, anovel ratio control or ratio change mechanism, a novel workheadassembly, novel means for conveying gears or gear blanks to the cuttingstations and transferring them between cutting stations with novel meansfor automatic stock division in going from one station to the other, anovel control means for controlling the operation of the work loadingand unloading and automatic stock division mechanisms, a novelchamfering means designed to remove burrs, etc. from the roughed gears,and other novel structures and techniques, all of which are beingcovered in a series of patent applications. These applications are: Ser.Nos. 764,212, 764,213, 764,214, 764,221, 764,222, 764,217, 764,218,764,219, 764,220, 764,215, and 764,216, filed Oct. 1, 1968, and thedisclosures of which are all incorporated herein by reference.Application Ser. No. 764,215 issued on June 14, 1970 as US. Pat. No.3,520,227.

While the present development relates especially to the production ofbevel pinion gears for the automotive industry, for example, spiralbevel or hypoid gears, it will be apparent to those skilled in the artthat features of the development may be used in machines for makingother types of gears, and for industries other than the automotiveindustry.

An object of the present invention is to provide novel processes andtechniques for the rough cutting of bevel gears, particularly spiralbevel or hypoid gears, and especially adapted to produce roughed gearsin less time for a higher production rate and at a lower overall cost ofproduction per roughed gear than in previous methods.

In the illustrative embodiment of the invention, to be described in moredetail hereinbelow, it will be seen that there is provided a novelpreliminary or first-stage roughing operation, and a novel combinationof that first stage roughing operation with a second stage roughingoperation wherein the second stage roughing operation preferablyincludes structures and techniques as disclosed in the copendingapplication of Hunkeler et al., Improvements in Ratio-Change and Set-Over Mechanisms in Bevel Gear Making Machines," Ser. No. 764,214 filedon Oct. 1, 1968. This combined, two-stage roughing operation is designedto produce roughed pinions in less time and with less cutter wear thanin previous machines, and, further, it is especially designed to beutilized in combination with a two-stage finishing operation, withautomatic loading and unloading of gear blanks and automatic transfer ofwork between the two roughing stages, and between the two finishingstages, as disclosed in the copending applications of Helfer et al.,"Apparatus for Transferring Work Blanks and Work Pieces in Bevel GearMaking Machines, Ser. No. 764,219 and Hunkeler et al., Control Apparatusfor Checking and Controlling Sequential Machine Operations, Ser. No.764,220 both filed on Oct. 1, 1968. In this combined, two-stage roughingoperation, cutting action will be taking place simultaneously on twodifferent workpieces, one at each roughing station.

In the first stage roughing operation, as contemplated in the presentinvention, the tooth slot that is produced is left shallow, that is tosay, it is not cut to the full depth desired for the final roughed gear,and this enables a cutter to be utilized with cutter blades ofsubstantially larger point width than was practicable in the past,whereby, among other advantages, the cutter blades will have a longerlife and will be stronger so as to enable better and faster cuttingaction. In the exemplary embodiment of the invention, the first cuttingaction in the first stage roughing operation will be a plunge cutperformed at or in the region of the heel of the workpiece, andthereafter there will be a forward generating roll during which acutting action will take place, and this generating roll will becurtailed or abbreviated, including only a central portion of the rollthat would otherwise have been required if the roughed tooth slot wereto be cut entirely during generation and in a generating roll.

This abbreviated generating roll of the first stage roughing of thepresent invention will thus enable the time for the cutting cycle to beshortened, as will be understood. The relative depth or plunge feedbetween the work and tool is utilized at the start of cutting any toothslot and provides for getting into the desired, partial depth beforestarting generation, as will be understood. After the forward generatingcutting roll is completed, there will be a return roll, as isunderstood, and this return roll preferably is effected without anycutting action during the first stage roughing, and there will berelative withdrawal between work and tool, and indexing of the work,after which the first stage roughing action will be repeated for thenext tooth slot, and so on, until the workpiece has completely receivedits first stage roughing.

1n the preferred embodiment, this first stage roughing will beaccomplished without utilizing a ratio change mechanism or any of theset-overs, as disclosed in the copending application of Hunkeler et al.,lmprovements in Set-Over and Setover Mechanisms in Bevel Gear MakingMachines, referred to above. Thus, in the first-stage roughing, thegeneration may be advantageously altered or set up so as to produce asuitable average shape for the tooth slots, in view of the furtherroughing operation to be performed thereon at the second roughingstation.

It is thus a further and more specific object of the invention toprovide a first-stage roughing operation in bevel gear making whereinthe rate of depth feed, rate of generation, and ratio of time spent forthese motions may be optionally controlled to achieve minimum productiontime and maximum cutter life. For producing gears having short face anddeep teeth, the first stage roughing operation will involve mainlyplunge or depth feed and little generation, as will be understood.Conversely, for producing gears having long face and shallow teeth,there will be a larger percentage of generation. Furthermore, the depthof the first stage rough cutting and the amount of the cutting rollutilized preferably will be designed so as approximately to balance thecutting time and cutter wear with the subsequent second stage roughcutting operation.

Further objects and advantages of the invention include the following:the first stage roughing operation will be highly efficient since themajority of the metal may be removed using a tool, or cutter blade, ofwide point width that is not only inherently stronger than those withnarrower point widths, but also is able to conduct heat away from thetip of the cutter blade more efficiently, resulting in lower tiptemperatures, more efficient cutting operation, and longer cutter life;because of the shallow slot in this first stage roughing operation, thecoolant is better able to reach the cutting zone,

providing for a more efficient and effective overall cutting action; thesecond stage roughing operation can be now performed at higher speedswithout undue cutter wear by reason of the fact that the greatest partof the material has already been removed in the first-stage roughingoperation, and furthermore the relatively shallow cut from the firstroughing stage will permit good coolant penetration to the cuttingregion during the second-stage roughing operation; and the second-stageroughing operation may advantageously be designed to have a controlled,nonuniform rate of generating roll in order to accommodate thenonuniform stock left by the abbreviated generation in the first stageroughing, and the second stage roughing may also advantageously bedesigned to utilize the ratio change mechanism, cradle rotationalsetover,

cradle axial setover and hypoid offset setover as disclosed in theabovetmentioned copending application of Hunkeler et al., (Improvementsin Ratio-Change and Setover Mechanisms in Bevel Gear Making Machines"),referred to above.

In the illustrative embodiment of the invention, the two roughing stageswill be shown and described as being provided by a double roughingmachine of the type disclosed in the copending application of Hunkeleret al., (Improvements in Ratio-Change and Setover Mechanisms in BevelGear Making Machines"), with certain modifications to the first roughingstations, as will be referred to below, and with a conveyor means forfeeding gear blanks to the machine, and with automatic work loading andunloading at the two roughing stages or stations, and automatic worktransfer between the two stages with automatic stock division, and withsubsequent depositing of the final roughed gears at a discharge region,for example, back on the conveyor means, as disclosed in the copendingapplications of Helfer et al., "Apparatus for Transferring Work Blanksand Work Pieces in Bevel Gear Making Machines, and Hunkeler et al.,Control Apparatus for Checking and Controlling Sequential MachineOperations," filed on Oct. 1, I968. Thus, a high speed and highlyautomated production process will be provided wherein roughed gears willbe produced at higher production rates, in less time, and at loweroverall costs. Additionally, it is also contemplated, in theillustrative embodiment of the present development, that the roughedgears be transferred to a double finishing machine of the type disclosedin the copending applications of Hunkeler et al., (Improvements in BevelGear Making," Ser. No. 764,2l2), Helfer et al. (Apparatus forTransferring Work Blanks and Work Pieces in Bevel Gear'Making Machines")and Hunkeler et al. ("Control Apparatus for Checking and ControllingSequential Machine Operations), filed Oct. 1, 1968, after beingchamfered by a suitable chamfering means, such as that disclosed in thecopending application of Hunkeler et al., (Chamfering Means," Ser. No.764,216), filed on Oct. l, I968, whereby a more fully automatedproduction line will be provided for producing finished gears,especially spiral bevel or hypoid pinions, from gear blanks. Because ofthe high speed operation of the double finishing machine, it will alsobe desirable to have a high production rate for the double roughingmachine, and the present invention provides a first-stage roughingoperation and a combined first and second-stage roughing operationeminently suitable to be utilized with the high speed double finisher,of the type referred to above and with a production rate coordinated tothe production rate ofthe double finisher.

It might be noted that the improved efficiency of the twostage roughingmethod of the present invention over previously proposed methods forcompletely roughing gear blanks in one roughing stage, (for example, asdisclosed in the Krastel et al., Pat. No. 3,288,031) derives primarilyfrom separating the two basic functions, namely, metal removal and shapecontrol, into two separate operations in which each can be performedoptionally, and effecting this separation in such a way that the cuttingtime may be advantageously equal for the two stages so as to permitcombining the two stages in a single automatic machine, as referred toabove.

Further objects and advantages of the invention will be in part obviousand in part pointed out hereinafter.

The novel features of the invention may best be made clear from thefollowing description and accompanying drawings in which:

FIG. I is a perspective view of a gear blank having a partial tooth slotformed therein by a plunge feed between the work and tool, according toa process of the present invention;

FIG. 2 is a photograph of a workpiece, corresponding to FIG. I, andillustrating a plurality oftapered tooth slots as they would appearafter being formed by a first stage roughing operation embodying theinvention;

FIG. 3 is a photograph, corresponding to FIG. 2, and illustrating aworkpiece after being subjected to two successive roughing operations,at two separate roughing stations and according to the presentinvention;

FIG. 4 is a schematic view of a tooth slot, in elevation, andillustrating the extent or amplitude of generation necessary to roughcut a slot of that length and shape by generation alone;

FIG. 5 is a schematic view corresponding to FIG. 4 and illustrating acombined plunge cut and generating roll for the first stage roughingoperation, embodying the invention, and showing by comparison with FIG.4 the abbreviated or shortened amplitude of generation permitted or madepossible by the present invention;

FIG. 6 is a view corresponding to FIG. 5 and illustrating a generatingaction as would be contemplated in the second stage roughing operationand indicating the amount of stock left at the bottom of the tooth slotat the end of the first-stage roughing operation and which will beremoved during the second roughing stage;

FIG. 7 is a schematic plan view, on a reduced scale, illustrating asingle roughing machine that may be utilized in practicing the firststage roughing operation of the present invention;

FIG. 8 is a schematic plan view, again on a reduced scale, illustratinga double machine that may be utilized to provide two finishing stationsfor firstand second-stage finishing operations;

FIG. 9 is a schematic plan view, again on a reduced scale, illustratinga double roughing machine and a double finishing machine that may bearranged together to provide a singleproduction line, wherein the doubleroughing machine will be utilized to practice the novel rough cuttingprocesses of the present invention;

FIG. 10 is an enlarged diagrammatic view of a generating train andcontrol arrangement therefor that may be utilized in practicing thepresent invention;

FIG. 11 is an enlarged and fragmentary schematic plan view ofa portionof the ratio control means as shown in FIG. 10;

FIG. 12 is an elevational view of the structure as shown in FIG. 11;

FIG. 13 is an enlarged elevational view corresponding to FIG. I2 andshowing more of the structural details;

FIG. 14 is an enlarged view corresponding to FIG. I] and showing more ofthe structural details;

FIG. I5 is an enlarged view of the structure shown in FIG. l3 and viewedin the direction of arrows 15-15 in that figure;

FIG. 16 is an enlarged, fragmentary and partially vertically sectionedview of a hypoid offset setover designed for use in the second stageroughing operation;

FIG. 17 is a fragmentary perspective view showing certain parts of thehypoid offset setover construction of FIG. 16;

FIG. 18 is an elevational view of structure designed to be utilized inthe cradle axial setover mechanism in the second stage roughingoperation;

FIG. 19 is an enlarged elevational view of the structure shown in FIG.18 and partially sectioned along the line 19-19 in FIG. 18;

FIG. 20 is a schematic and diagrammatic view of an exemplary hydrauliccontrol arrangement for the ratio change mechanism and various setovers,referred to above, in the second stage roughing operation.

DETAILED DESCRIPTION Referring now to the drawings, FIG. 9 shows twodouble gear cutting machines 20, 22 illustrative of automatic pinionmachines of the present development, as described in the copendingapplication of Hunkeler et al., Improvements in Bevel Gear Making,"referred to above. The machine 20 is a double finishing machine whereineach of the cutting stations has a finishing operation performedthereat, while the machine 22 is a double roughing machine illustrativeof a machine in which the novel rough-cutting processes of the presentinvention may be utilized. The roughing machine 22 is shown as includingtwo cutting stations 24a, 24b arranged on a suitable frame means, andwherein each cutting station includes a cradle housing 30 containing thecradle 32 and toolholder 34 (shown in FIG. with the cradle housingmounted for adjustable movement on the base frame means,

as disclosed in the copending applications of Hunkeler et al.,

Improved Cradle Assembly for Gear Cutting Machines and Means for MovingCradle Axially," Ser. No. 764,222, Means for Supporting Cradle andCradle Housing," Ser. No. 764,221. The toolholder 34 is mounted forrotation within the cradle 32 and about a horizontal axis which may beadjusted within a certain range or ranges of positions, as will beunderstood. The toolholder is designed to mount a rotary face millcutter and the rotary toolholder, face mill cutter and adjustable meansin the cradle for adjusting the position and angle of the face millcutter and rotary toolholder may be conventional, as disclosed, forexample, in U.S. Pat. No. 2,667,818.

The double roughing machine 22 is shown as including upstanding flangesor sidewalls 36, 38 suitably mounted on the base frame means andextending upwardly therefrom. A workhead assembly 40 is mounted betweenthese sidewall members and includes a rotatable workholder 42 mountedtherein and designed to receive the work that is to be cut so that thework is rotatable about a vertical or generally vertical axis, as isdisclosed in the copending application of Hunkeler et al., WorkheadAssembly and Mounting Therefor, in Bevel Gear Making Machines," Ser. No.764,221.

In the copending application of Hunkeler et al., Improvements in BevelGear Making, the double finishing machine is shown as being of the sameor of a similar design to the double roughing machine 22, except forcertain structural modifications therein adapting it for finishingrather than roughing, as will be understood to those skilled in the art,and as will be apparent from the series of applications covering thepresent development, as referred to above and filed on Oct. 1, I968.Thus, like reference numerals have been utilized in FIGS. 8 and 9 todesignate corresponding parts of the double roughing and doublefinishing machines. FIG. 7 illustrates a single roughing machine,similar to the upper half of the double roughing machine 22 shown inFIG. 9, and also embodying the present development, wherefore likereference numerals have again been utilized to designate like parts.

The novel processes of the present invention for first-stage roughingand for combined first and second stage roughing are especially designedto be utilized in combination with a double roughing machine such as themachine 22 shown in FIG. 9 and disclosed in the series of copendingapplications referred to above; however, it will be understood thatthese novel rough cutting processes and the principles involved therein,or portions thereof, may be practiced in a single roughing machinehaving only a single cutting station, such as the single machineillustrated in FIG. 7. Additionally, these same novel rough cuttingprocesses and principles involved therein may be practiced in whole orin part in connection with roughing machines other than the specificroughing machines shown in FIGS. 7 and 9, as will be understood.

As disclosed in the copending application of Hunkeler et al.,Improvements in Ratio-Change and Setover Mechanisms in Bevel Gear MakingMachines," there is provided a novel ratio change mechanism, and a novelcombination of setovers, including cradle rotational, cradle axial, andhypoid offset setovers, which may be utilized in roughing operations.According to the present invention, that ratio change mechanism andthose setovers preferably are utilized only in the second or finalroughing operation, and may be, and preferably are, entirely omittedfrom the first stage roughing, as will be described in more detailhereinbelow, with the accompanying advantages of a more simplifiedconstruction with fewer parts for the generating train and associatedstructures in the first roughing station.

THE DRIVING ARRANGEMENT It will be understood that in generation ofbevel gears, such as spiral bevel or hypoid gears, there commonly aretwo basic elements, the cradle and the work spindle, both of these beinglocated in a certain spaced relationship with one another and rotatingin a predetermined timed relationship on their respective axes.conventionally, the cradle carries a rotating, multibladed face millcutter (not shown) whose axis is in ad- 10 justable but stationaryposition relative to the cradle, offset from and generally inclined tothe axis of the cradle on which it is mounted. The cradle and cuttermounted thereupon represent the imaginary generating gear," as isunderstood, and the rotating cutter blade edges represent a tooth ofthis imaginary generating gear." The work spindle carries the work beingcut; the cradle carrying the cutter rotates about the cradle axis intimed relation to the rotation of the work spindle with the rotatingcutter in engagement with the work. Thus the imaginary "generating gear"is said to roll with the workpiece.

The roll proceeds sufficiently to complete the generation of one toothslot (or in some cutting operations, one side of one previously roughedtooth slot), whereupon there is a withdrawal so that the cradle with itscutter and the work are relatively separated one from the other in thedirection of the cradle axis. The rolling motion of both cradle and workspindle is reversed during which time an increment of motion is added tothe work spindle such as to advance (index) the work relative to thecradle by one pitch. At the completion of the reversal of roll, calledthe return roll, relative cradle axial movement between cradle and workagain occurs to bring the two into cutting position, whereupon a cycleis repeated to cut the following tooth. It will be understood that, ifdesired for certain cutting operations, a cutting action could beprovided on the return roll, after which the cutter and work will berelatively withdrawn, and the work indexed for the next toothcuttingcycle.

THE GENERATING TRAIN The generating train of the machine, as will beunderstood, is the complete connection between the cradle and workspindle for controlling the relative generating rotation of these twomembers. The illustrative embodiment of the generating train shown inFIG. 10 will now be traced. A worm gear 52 is fixed rotationally to thecradle 32, and this gear is engaged by a worm 54 connected to atelescoping shaft 56 on which is mounted a change gear 58. This is thepoint in the train where there is introduced a set of four change gears,a selection of which governs the ratio of generating roll between thecradle and work. Continuing through this latter set of change gears 60,62, 64 through shaft 66, there is a connection to a suitable indexdifferential gearing 68. Except during the indexing interval, which willbe referred to again hereinbelow, the index differential 68 can beregarding as a simple train of gearing with gear 70 meshing with gear 72which is rigidly connected to gear 74 meshing with a gear therebelowrigidly connected to gear 76 which in turn meshes with gear 78, asshown. Gear 78 is rigidly connected to or integral with bevel gear 80,in turn meshing with bevel gear 82 connected to shaft 84.

Shaft 84 is keyed for rotation to another bevel gear 86 engaging with amating gear 88 fastened to a shaft 90 which is connected for rotation toa pinion 9-2 of a hypoid pair. The meshing hypoid gear 94 is rigidlyconnected to the work spindle. As will be understood, the work spindleis connected for rotation in the workhead assembly 40. This completesthe trace of the generating train, that is, the gearing which links andcontrols the relative rotational motion of cradle and work during thegenerating rolls. It will be understood that this generating train willbe capable of being rotated in either direction, for the forward andreturn rolls.

There will be a separate generating train, servocontrol arrangementtherefore, and associated structures, (shown in FIG. 10), for eachroughing station, as indicated in the copending application ofI-lunkeler et al., Improvements in Bevel Gear Making.

THE INDEXING MECHANISM A suitable indexing mechanism 96 will beprovided, and in this connection, reference is made to U.S. Pat. Nos.3,229,552 and 3,283,660, the disclosures of which are incorporatedherein by reference. The teachings of those patents indicate suitableindexing mechanisms that may be utilized in part in connection with thegenerating train, in the present invention. In an indexing step, thecradle 32 may be considered as fixed against rotation, and likewisecradle gear 52, worm 54 and related elements of the generating train, aswill be evident. In the operation of the index 96, an index rack 98 willbe moved in a direction perpendicular to the plane of the diagram inFIG. and through a fixed distance by a suitable hydraulic piston (notshown). The rack 98 engages a pinion 100 which is made to turn exactlyone revolution as a result of the controlled distance of rack travel.Pinion 100 drives a gear 102 through an axially engageable anddisengageable one tooth clutch 104. During the forward or indexingstroke of the rack, clutch 104 is held in engagement by hydraulicpressure in cylinder 105, as will be understood. One turn of gear 102produces a corresponding single turn of mating gear 106, which producesone turn of the coaxial and connected change gear 108. During theindexing motion of gears 106 and 108, a locking pawl 110 is made todisengage from a notch in a locking disc 112 connected to andcorotatable with the gears 106 and 108. At the completion of the oneturn, the locking pawl is made to reengage disc 112.

The change gear ratio 108, 114 is so chosen that an appropriaterotational increment is produced in the gear 114, producing in turn theidentical increment in the connected differential spider 116. Spider 116carries the differential pinions around the stationary gear 70. Theaction of the differential is such as to produce a turning of gear 78relative to gear 70, equal to exactly twice the turning increment of thespider 116. The appropriate rotational increment in gear 114, controlledby the index change gear selection, must be such that the amount ofturning of differential gear 78 relative to differential gear 70 willproduce, by way of generating train elements 78 through 94, an incrementof work spindle turning relative to the fixed cradle equal to one pitchof the work.

It will be recalled that for the purpose of explaining the function ofthe indexing mechanism, the cradle was considered as fixed rotationally.In actual operation, however, the indexing can be made to occur whilethe cradle is turning as, for example, during the noncutting portion orreturn roll of the cycle. The increment of index rotation produced inthe work relative to the cradle is the same.

At the completion of one indexing step, hydraulic pressure in cylinder105 will be released permitting disengagement of clutch 104 and the rack98 and pinion 100 will be returned to their original position, beforethe clutch is reengaged.

THE DRIYE FOR THE GENERATING TRAIN As shown in FIG. 10, the drive forthe generating train includes a reversible hydraulic motor 118, drivingthrough shaft 120 and roll change gears 122, 124 and fixed gearing 126,128, the latter gear being rigidly attached to shaft 66 in thegenerating train. A controllable displacement, hydraulic pump 132 isshown as being connected to the hydraulic motor for controlled andreversible driving actuation thereof in conventional manner. The pump132, in turn, is driven by a motor 134, which in the illustrativeembodiment is a constant speed electric motor. The electric motor 134,hydraulic pump 132, and hydraulic motor 118 and the various drivingconnections therefore may all be ofconventional design.

THE CUTTER DRIVE The cutting tool, toolholder 34, and the cutter drivetrain are shown in FIG. 10 as driven by a separate power source, for

example, an electric motor 177, through speed change pulleys 179, 181and belt 183, and a train of gearing 185 within the cradle. This gearingmay be of conventional design as disclosed, for example, in U.S. Pat.Nos. 2,667,818 and 3,288,031.

CONTROL SYSTEM FOR THE DRIVE TRAIN The present development contemplatesa novel control system for the drive train in combination with the novelstructural orientation of the cradle housing, cradle, toolholder andworkhead assembly, as referred to above. The control system, per se, ismore fully disclosed and claimed in the copending application ofHunkeler et al., (Improvements in Control Arrangements for Bevel GearMaking Machines, Ser. No. 764,213).

The illustrative embodiment of the control system, as best seen in FIG.10, includes a servomechanism 136, comprising a variable speed DC motor138 driving through belt 140 and pulleys 142, 144, and through rightangle gearing 146, 148 to a worm 150 which in turn is drivingly engagedto a worm wheel 152. The worm wheel 152 is fixed to and rotates maincamshaft 154 which is mounted for rotation suitably in a feed cambracket (not shown) rigidly attached to the machine frame. The feed camshaft 154 carries the feed cam 156, various hydraulic 158 and electrical160 trip cams (for various purposes, such as producing appropriatetiming for such functions as hydraulic pressure and release to theindexing mechanism, ratio control and various setovers as will beunderstood). A rise end cam, called a roll cam 162, is also driven bythe cam shaft 154. The variable speed motor 138 will be adjusted toregulate the cycle time of the entire machine. In the present embodimentof the invention, one turn of the main camshaft 154 will produce onetooth cutting cycle.

A roll cam follower roller 164 is mounted on a nut 166 ofa nut and screw168 assembly, constituting a differential connection between the camshaft 154 and the generating train, as will be apparent. The nut will beconstrained against rotation but is free to translate or move axially.The screw 168 is free to translate axially and to rotate within thenonrotating nut 166, and the lower end of the screw, as shown in thedrawing, bears on or against a pivoted lever 170, the free end 172 ofwhich is arranged to actuate a hydraulic control valve system 173, ofconventional design, and which includes a wobble plate valve (notshown). The wobble plate valve is designed to govern the direction andflow rate of the discharge of the pump to the hydraulic motor, and thisestablishes the direction and rate of motor rotation, as is understood.

A compression spring 174 is shown continuously urging the actuator andscrew 168 upwardly, as shown in FIG. 10, so as to urge the follower 164into engagement with the roll cam 162.

When the cam 162 rotates from the position shown in FIG. 10, thefollower 164, nut 166, screw 168 and actuator 170 will tend to moveupward, as viewed in FIG. 10, as urged by the spring 174.

This movement will result in a valve movement permitting the pump todischarge fluid (for example, oil) at a certain rate and such as torotate the motor 118 in the direction shown by the arrow. Fixed forrotation with the motor output shaft 120 is a gear 176 which is engagedto gear 178 fixed for rotation with screw 168. Rotation of the motorresulting from movement of the pump control valve regulating flow of thedriving fluid to the motor will thus effect rotation of the screw 168through the gears 176, 178, such that the screw 178 will thread itselfdownward within the nut 166 and tend to restore the lever 170 andcontrol valve 173 to their original or neutral position. The lever andcontrol valve will be restored to that neutral position unless furtherfalling of the cam path, permitting further upward movement of the nut166, results in a command for continuous discharge from the pump 132 tothe motor 118. The pump 132 and motor 118 will both be of the positivedisplacement type, in the illustrative embodiment and thus it will beseen that a given rise or fall of the cam will produce a correspondingfixed number of turns of the motor 118, and the established rise of thecam 162 will produce a fixed number of turns each way of the shaft 120per tooth cutting cycle.

Selection of the appropriate roll change gears 122 and 124 produces fromthe fixed number of turns of the shaft 120 a desired angle of turning inthe work spindle, as required to fully generate one tooth contour.Selection of the ratio of roll change gears 58, 60, 62 and 64 in thegenerating train will produce the proper proportionate angle of cradleturning, as will be apparent. Thus, by suitable choice of these rollchange gears and ratio of roll change gears the desired amount of rollfor the work spindle and cradle can be predetermined, for cxample,depending upon the requirements of a particular cutting operation andcycle. However, the present development also contemplates a separate andnovel means for effecting a change in this ratio of roll between thecradle and work spindle during operation so as to produce a differentratio of roll in one direction of roll than in the other direction ofroll, as may be desired for certain cutting operations, for example, inthe generation of spiral or hypoid pinion gears. This means for changingthe ratio of roll, separate from the ratio or roll change gearsmentioned above, will be described in more detail hereinbelow.

The feed cam 156, operating from the main cam shaft 154 for cyclecontrol, preferably is arranged to actuate the cradle 32 axially towardand away from the work, as is disclosed in the copending application ofHunkeler et al., Improved Cradle Assembly for Gear Cutting Machines andMeans for Moving Cradle Axially.

It will be understood that the generating train, servocontrol mechanism136 therefor, and the associated structures illustrated schematically inFIG. 10 preferably are duplicated for each of the two roughing stationsand each of the two finishing stations of the double machines 20, 22, asindicated in the copending application of Hunkeler et al., Improvementsin Bevel Gear Making."

PRELIMINARY OR FIRST STAGE ROUGHlNG According to the present invention,novel processes and techniques are contemplated for the first stageroughing operation which, in the illustrative arrangement of FIG. 9, maybe performed at station 24b in machine 22. As indicated above, theseprocesses include starting the cutting of a tooth slot with a plungefeed effected between the tool and work piece W, with the tool firstentering the workpiece at or in the region of the heel H thereof andonly going to partial depth, that is, not to the full depth desired forthe final roughed tooth slot. FIG. 1 illustrates a pinion gear blankhaving partially formed tooth slot S therein illustrative of the type ofcut that may be effected by this plunge feed or plunge-type cutting. Aswill be understood, there is no rolling or generating between the tooland the workpiece for this initial, plunge cut. It will be effected insuitable manner, for example, by appropriate design of the feed cam 156,as will be understood from the disclosure of the copending Hunkeler etal., application 1mproved Cradle Assembly for Gear Cutting Machines andMeans for Moving Cradle Axially, referred to above. As disclosed in thatapplication, the feed cam 156 is operatively structurally connected tothe cradle to move it axially toward and away from the work and suchstructure preferably will be utilized with the feed cam 156 in thepresent invention and properly designed to effect the desired axialmovements ofthe cradle (and the tool with it) toward and away from thework for the plunge feed, initial cut, and for withdrawal in connectionwith indexing, as will be evident.

After the plunge cut to partial depth has been completed, a forwardgenerating roll toward the toe T will take place, during which a cuttingaction is effected. ln this cutting, generating roll, in the methodcontemplated, there will be cutting on both the convex and concave sidesof the tooth slot, and the tooth slot will be extended to the toe of theworkpiece as shown, for example, in FIG. 2, whereby a first roughedtooth slot will be provided in an efficient and expeditious manner. inthe illustrative arrangements shown in FIGS. 1 and 2, the plunge cutextends from the heel H of the workpiece a substantial distance towardthe toe T so that the amplitude or extent of the generating rollfollowing the plunge cut will not extend over substantial distances.However, as indicated above, the relative amounts of material removed bythe plunge cut on the one hand, and the cutting generating action on theother, may be varied, as desired, depending upon factors such as thedesign requirements of the final tooth shape, the number of teeth to becut, etc.

The shape of the roughed out tooth slot formed by the first stageroughing operation can be seen in FIG. 2. It will be noted from thisfigure that there is an unequally divided amount of stock yet to beremoved from the convex and concave sides of the teeth to produce thefinal roughed tooth shape. Thus, during the second-stage roughingoperation, to be described in more detail hereinbelow, it will benecessary to remove sufficient and unequal amounts of material from theconvex and concave sides of the teeth so as to produce the desiredtapered configuration for the final roughed tooth slots. FIG. 3illustrates an exemplary configuration of a workpiece that has beensubjected to both a first and a second-stage roughing operationaccording to the invention.

The generating cutting action in the first stage roughing operation,following the initial plunge feed between tool and work, will beeffected in suitable manner, for example, by means of appropriate designof the roll cam 162 of the servocontrol mechanism 136, as will beunderstood. This servocontrol arrangement is disclosed in more detail inthe copending Hunkeler et al., application Improvements in ControlArrangements for Bevel Gear Making Machines.

Still referring to the first stage roughing operation, when the forward,cutting, generating roll, just referred to, has been completed, therewill be the usual return roll, relative 'withdrawal between tool andworkpiece, and indexing of the workpiece to move the latter intoposition for the next tooth slot to be cut, as will be understood. It ispreferred that no cutting action take place during this return roll,whereby the return roll may be effected at higher speeds and in lesstime (once again, by suitable design of the roll cam 162), and relativewithdrawal between cradle and work and indexing of the work may,therefore, be effected at some suitable time (as by appropriate designof the feed cam 156) so as to advantageously cut down or reduce thetotal cycle time.

After the work has been indexed, in the first stage roughing operation,there will be a partial generating roll (without cutting) prior to thenext plunge feed for the purpose of eliminating backlash in thegenerating train so that in the subsequent cutting, generating roll,proper cutting action may be achieved. In other words, there will be noundesirable dwell time at the end of the plunge feed (gashing cut) andbefore the generating cutting action, referred to above. Thus, thepartial roll (without cutting) will be advantageously instantaneouslyresumed in the later cutting, generating roll at or about at the end ofthe plunge feed (gashing cut).

After this partial roll, there will again be relative plunge feedbetween the tool and work to effect a plunge cut at or in the region ofthe heel of the workpiece and to partial depth, as discussed above. Inthe illustrative arrangement of roughing machine shown in FIGS. 7, 8, 9and 10, the feed cam 156 will be so designed to effect this plunge feedat the proper time and to the desired depth. Thereafter, the generatingtrain will again be activated through the roll cam 162 of theservomechanism 136 so as to provide a cutting generating roll betweenthe work and tool, as understood. Thus, in the exemplary roughingmachine arrangement, the roll cam 162 and feed cam 156 will be sodesigned as to effect the proper timed relationship between the plungefeed and the cutting, forward generating roll. And in view of the factthat the cutting generating roll is abbreviated in amplitude,.asdiscussed above, this roll may be accomplished in a relatively shorttime, as by proper design of the roll cam 162, again so as to cutproduction time.

As indicated above, at the end of the forward cutting roll, there willbe the return roll, relative withdrawal between the work and the tool,and work indexing. The roll cam 162 may be so designed as to effect thisreturn roll in an even shorter time than the forward generating rollsince there will be no cutting on the return roll. Thus, in the firstroughing stage, there is no need for any ratio-change mechanism, nor isthere any need for any of the setover mechanisms, such as disclosed inthe copending application of Hunkeler et al., Improvements inRatio-Change and Set-Over Mechanisms in Bevel Gear Making Machines, andthese structures may therefore be advantageously omitted from the firststage roughing machine.

Inasmuch as there is no cutting on the return roll, the feed cam I56 maybe so designed as to begin withdrawal of the eradle and tool during thatroll, whereby the work may be indexed sooner than if it were necessaryto wait for the return roll to be completed before indexing the work,thus providing a further reduction in the cycle time.

For the sake ofindicating the type of cutting action contemplated in thefirst and second stage roughing operations according to the invention,and comparing them with a conventional single stage, complete roughingoperation, reference will be made to FIGS. 4, and 6. FIG. 4 illustratesschematically a tooth slot defined by the numbers 1,2,3 and 4. Thistooth slot (which would be tapered for spiral bevel and hypoid gears)corresponds to the final roughed tooth slot desired, before a finishingoperation, and it is illustrated as being cut entirely by a generatingroll wherein the amplitude of the generating roll is indicated by thedistance marked by the legend Generation in that figure. It will benoted that the position of the cutting tool in FIG. 4 at the start ofthe generating roll is indicated schematically by centerline C, and thecurved line M, as being sufficiently far to the right of the heel H soas'to begin the cutting action at the heel, and the generating rollcontinues to the toe of the slot wherein the center line of the cutteris indicated schematically as C,. This would correspond to so-calledratio-change roughing for tapered tooth slots where on the return rollthe ratio of roll between the tool and work would be varied, forexample, as disclosed in the Wildhaber Pat. No. 2,342,232, and withcutting action going on during both rolls, as is understood.

FIG. 5 illustrates schematically the first stage roughing operation ofthe present invention wherein the centerline C, indicates schematicallythe position for the cutting tool at the beginning of the plunge feed,and the distance identified; by the legend "Plunge Cut" indicates thecutting distance covered by the plunge feed, after which generation willbegin and will continue until until the centerline of the tool reachesthe position indicated by C in that figure. After the centerline of thetool reaches the position indicated schematically by C in FIG. 5, therewill be relative withdrawal between the workpiece and the tool afterwhich there will be a return roll. This return roll will terminate shortof the roll out point of generation at the heel (12), as indicated. Itwill be noted that the amplitude of generation in this first stage issubstantially less than the amplitude of generation indicated in FIG. 4,and furthermore, the plunge cut does not go to the full depth of thedesired final roughed tooth slot, but a certain amount of material isleft, as indicated by the crosshatching in the region 1, I, 4, 4 in FIG.5. Furthermore, it will be appreciated that the forward and returngenerating rolls each advantageously terminate short of the roll outpoints of generation at both the heel and toe of the workpiece, asclearly shown in FIG. 5.

FIG. 6 illustrates the second stage roughing operation according to thepresent development, and here again it will be noted that the amplitudeof generation is still less than the amplitude of generation required inthe conventional method, illustrated in FIG. 4, inasmuch as the toothslot has already been partially cut. During the second stage roughing,the

amount of stock indicated by crosshatching in FIG. 5 will be removed, aswell as material on the convex and concave sides of the tooth slots, soas to produce the final, roughed tooth shape, an exemplarlyconfiguration of which is illustrated in FIG. 3. However, it will beunderstood that the relative amounts of plunge cut and generation forthe first stage roughing may be varied as desired, and the second stageroughing operation, in the illustrative arrangement under consideration,preferably includes the ratio-change mechanism and setovers disclosed inthe copending application of I-Iun keler et al., referred to above, aswill be discussed in more detail hereinbelow.

AUTOMATIC LOADING AND UNLOADING AND STOCK DIVISION It is alsocontemplated in the present invention that conveyor means and aloader-transfer mechanism be provided for automatically conveyingworkpieces to the machine, automatically loading them onto the workholder at the first roughing station, automatically transferringworkpieces, after receiving preliminary roughing, to the second roughingstation to be subjected to a second roughing operation, and thereafterautomatically transferring the workpiece to a discharge region.Additionally, it is contemplated that automatic stock division takeplace in moving the workpiece from the first to the second roughingstation, thus eliminating the need for any manual operations in theentire two-stage roughing cycle. Suitable structures and techniques foreffecting this automatic conveying, loading, unloading and stockdivision are disclosed in the U.S. Pat. to Hunkeler et al., No.3,520,227 granted July 14, 1970. Such a conveyor 44 and loader-transfermechanism 46 are shown in FIGS. 7, 8 and 9. The loader-transfermechanism is in the form of a turret having three arms and adapted to beperiodically rotated and vertically reciprocated in connection with thework loading and unloading operations and in coordination with thestep-by-step feeding action of the conveyor means 44, as disclosed inthe copending applications just mentioned.

In connection with the operation of the loader-transfer mechanism, itwill be noted that the workhead assembly 40 is designed in the presentdevelopment to undergo movements between a work loading and unloadingposition, on the one hand, and a work cutting position, on the otherhand, in timed relation with the operation of the loader-transfer turret46, as disclosed in the copending applications of Hunkeler et al.,workhead Assembly and Mounting Therefor, in Bevel Gear Making Machines,"and the Hunkeler et al. U.S. Pat. referred to in the precedingparagraph. Furthermore, and in connection with automatic stock division,as referred to above, it will be appreciated that the roll centeringdevice disclosed in the aforesaid copending application of Hunkeler etal. Improvements in Control Arrangements for Bevel Gear Making Machines"may be utilized.

SECOND-STAGE ROUGHING It is contemplated that the second stage roughingoperation performed, for example, at the second roughing station 24a ofthe double roughing machine 22 (see FIG. 9) will effect a stock removalfrom the convex and concave sides of the tooth slot and also from thebottom of the tooth slot, formed in the first stage roughing operation,so as to approximate more closely the desired, finished tooth shape, aswill be effected in the double finishing machine 20, for example, asdisclosed in the copending applications of Helfer et al., Apparatus forTransferring Work Blanks and Work Pieces in Bevel Gear Making Machines"and Hunkeler et al., "Control Apparatus for Checking and ControllingSequential Machine Operations." As indicated above, FIG. 3 illustratesan exemplary tooth configuration for the workpiece after it leaves thesecond roughing station, and by comparison with FIG. 2, an observationmay be made as to metal removed in the secondstage roughing operationfor the exemplary tooth configurations there shown.

RATIO-CHANGE MECHANISM AND ROTATIONAL SETOVER The structures andprocedures involved in the ratio-change mechanism and cradle rotationalsetover will now be described with reference being made to FIGS. 20, itbeing understood that these structures are designed primarily for use inthe second stage roughing operation, after the work has left the firstroughing station, and they may be advantageously omitted from the firstroughing station.

It is contemplated that the ratio-of-roll between cradle and work willbe determined for one direction of roll by the ratioof-roll change gears58, 60, 62 and 64, as shown in the drive diagram in FIG. 10. For thisdirection of roll, the ratio-change mechanism 188 will not have anyeffect on the roll, as will be apparent as the description proceeds. Forthe opposite direction of roll, however, the ratio-change mechanism willhave an effect on the roll, and as will be understood as the descriptionproceeds, it imparts an axial movement in a particular direction to thecradle drive worm 54 which will either add to or subtract from therotational motion of the worm gear 52 affixed to the cradle and causedto rotate through the generating train gearing and shaft 56 to thecradle worm 54.

Referring now to FIG. 10, it will be seen that the ratio control orratio-change mechanism includes a gear 198 driven by the gear 176 on theshaft 120 of the generating train. Gear 198 is connected through shaft199 to right angle gearing 200 and then through a train of gears 202 toa shaft 203. Shaft 203 includes a gear 205 at the other end thereof andin mesh with gear 207 on shaft 209. Shaft 209 includes a cam 206drivingly affixed thereto, as indicated. All of these parts will bearranged in suitable structures in the machines, as will be understood.

Referring now to FIGS. 10, 11 and 12, it will be seen that shafts 203,209 are journaled in a cam bracket 211 which is suitably arranged forpivoting about the axis of shaft 203 as a fixed axis and for a purposeto be described hereinbelow. The cam 206 is designed to be selectivelyurged against a cam follower roller 208 mounted for rotation in followerbracket 210, as best seen in FIG. 4. An end ofthe shaft 56 carrying theeradle worm 54 is shown suitably journaled in thrust bearings 214 heldwithin a retaining cartridge 215 connected to the follower bracket 210.Thus, back and forth motion of the follower 208 will control axialmotion of the worm 54. In this connection, bracket 210 is shown in FIG.13 as being slidably mounted in the worm bracket 216 ofthe cradlehousing 30.

A piston 218 is shown in FIG. 12 arranged in a cylinder 220 and carryinga member 222 at the upper end thereof and in engagement with the freeend 224 of the cam bracket 211, as shown. A fluid line 226 is shown asbeing connected to the cylinder 220, at the lower end thereof, for thetimed introduction of fluid pressure into the cylinder to elevate thepiston 218, and hold it in the position shown in FIG. 12. When thispressure is released, it will be appreciated that the piston will beurged down in the cylinder to its retracted position under the weight ofthe cam bracket 211, gear 207 and cam 206. But a yieldable compressionspring 228 is arranged in the cylinder 220, as shown in FIG. 6 to tendto hold bracket 211 in the position shown.

As shown in FIGS. 12 and 13, the follower bracket 210 will becontinuously urged to the right during cutting operations. In theillustrative embodiment shown, this is accomplished by means of fluid orhydraulic pressure in line 230 entering cylinder 232 and urging piston234 therein to the right against the follower bracket 210 so ascontinuously to urge the roller or follower 208 to the right and inengagement with the cam 206. This fluid pressure will be of suchmagnitude as to yield to the action of the cam surface of cam 206 whenthe latter tends to move the follower 208 and shaft 56 to the left asviewed in FIGS. 12 and 13, as will be appreciated. Piston 234 is shownas being slidably arranged in worm bracket 216 in the cradle housing,and a plurality of these pistons and cylinders 232 may be providedengaging the follower bracket 210 at several points to provide for amore uniform distribution of pressure thereon. A screw 236 is showncarried by the follower bracket 210 and engaged by the piston 234.

As will be understood, when the cam bracket 211 is held in the positionthereof shown in FIG. 12 by fluid pressure in the cylinder 220, the cam206 will be rotating in engagement with the follower roller 208.Rotation of the cam 206 will operate in conjunction with the fluidpressure in the cylinder 232 urging the roller 208 against the cam 206,to effect axial movement of the shaft 56 carrying the worm 54, inaccordance with the contour of the surface of the cam 206 so as toaffect the rotation of the worm gear 52 on the cradle 32, Cam 206 willbe so operative during the time it is desired to change the ratio ofroll between the cradle and work from what it would otherwise be underthe influence only of the ratio of roll change gears 58,60, 62 and 64 ofthe generating train. However, during a roll whenever it is desired tohave only these latter gears operate to determine the ratio of rollbetween cradle and work, the pressure in cylinder 220 will be released,and rotation of the cam 206 will noteffect any movement of the wormshaft 56. Thus, the ratio change mechanism 188 will be disabled or notactive during that particular roll. It is only when pressure isintroduced into cylinder 220 to hold the piston 218 elevated that theratio of change mechanism will be enabled or active to effect thedesired change in the ratio of roll.

Cylinder 220 may be suitably attached to the cradle housing 30 andpiston 218 is shown as having a collar 238 attached thereto by nut 240to provide a positive stop against the cylinder cap 242, for upwardpiston movement.

During the roll direction in which the ratio change mechanism isoperative, the axial position of the cradle worm will thus be under thecontrol of the ratio of roll cam 206 being rotated about its axis whichis held in a fixed position by the interaction of the piston 218hydraulically forced against the positive stop 242 and the followerroller 208 hydraulically forced against the cam surface by pistons 234acting against elements 210, 215.

The present invention also contemplates novel structures for effectingcradle rotational setover which may be used for size control, as will beunderstood. In the illustrative embodiment, and as seen particularly inFIGS. 11, 12, 13 and 14, this cradle rotational setover mechanism 244preferably is designed to operate instantaneously before the rollreverses at the end of the roll direction during which the ratio changemechanism 188 is enabled or active, and before the roll reverses to thedirection in which the ratio change mechanism is disabled. The structureof the cradle rotational setover means will then take control of thecradle worm axial position away from the ratio change cam 206, and willeffect an abrupt change in that position, that is, in the position ofthe cradle worm 54, thereby producing a corresponding abrupt change inthe cradle rotational position, for the purpose indicated.

As best seen in FIGS. 11, 12 and 13, there is provided a setover piston246 actuated by hydraulic pressure in cylinder 248 and which has itsaxial position moved alternately to the left, in FIG. 13, for onedirection of setover prior to the beginning of one cradle rolldirection, and to the right prior to the beginning of the oppositedirection ofcradle rolling. Suitable means are provided for adjustmentof the amount of travel available for the piston 246. As shown in FIG.13, this includes a hand adjusting wheel 250 which carries threadedelements 252 and 254 screwed in the piston, and a dial 251 is alsoprovided. The inner end of wheel 250 forms an adjustable gap with theadjacent facing shoulder of the cylinder 248. This total adjusted gapexists when the pressure in cylinder 248 is released and the piston 246is being held in a position fully to the right against the stop 256. Theforce to hold the piston to the right originates with the hydraulicpressure continuously present in cylinders 232 acting through pistons234 and bracket 210 and cartridge 215. Bracket 210 carries a stop plate258 designed to be engaged by the left end of a stop arm 260 which issuitably directly fastened to the piston 246, as shown.

The stop arm 260 travels axially with piston 246 and both are preventedfrom rotation by means of the arm 260, engaging in a slot 262 in thecradle housing 30 which preferably mounts both cylinders 220 and 248, asshown.

When pressure is admitted to the cylinder 248 through some suitablefluid port, the cradle rotational setover piston 246 will be moved tothe left, as viewed in FIGS. 11-13 until the inner end of wheel 250strikes the stop surface 262. This will effect a setover of the worm 54axially to the left, through the curved stop arm 260 and stop plate 258.Simultaneously pressure will be released from the cylinder 220 therebydisabling the ratio-change mechanism 188. For this part of the cycle,which may be either an up or a down roll as chosen, pressure will remainin the cylinder 248 and will remain exhausted from the cylinder 220.

The ratio-change cam 206 will continue to rotate, being driven by thegear 205, and the axis of the cam 206 will remain in the position shownifon a falling path ofits surface, or ifthe cam is rotating such as topresent a rising path to the follower 208, the cam bracket will merelylower against the light pressure of compression spring 228 in cylinder220, and in either case, the rotating cam will have no effect on theaxial position of the cradle worm at this time, and the pressure incylinder 248 will prevent axial movement of worm S4 to the right.

When pressure is then readmitted to the cylinder 248 approximatelysimultaneously with the next reversal of cradle roll, pressure will beexhausted from the cylinder 248. This release of the pressure in thelatter cylinder will permit movement to the right of the piston 246,stop arm 260 and cradle worm; however, it will be noted that such returnmovement of these parts may or may not take place depending, forexample, on the design and adjustment of the cam 206. In other words,ifa rising part of the cam is in engagement with the roller 208 at thistime, return movement of the roller to the right will be prevented. Cam206 will thus be urged by pressure in the cylinder 220 to return to orremain in the position thereof shown in FIG. 13 and established by thepositive stop 242 on the cylinder cap. Rotation of the cam will reversewith the reversal of cradle roll, and the cam will reassume control ofthe axial positioning and axial movement of cradle worm 54, as will beunderstood.

A suitable dial 264 and pointer 266 may be provided, as shown in FIGS.14 and 15, in connection with indicating and setting the position forcam 206, as will be evident.

CRADLE AXIAL SETOVER The illustrative embodiment of the cradle axialsetover mechanism is shown in FIGS. 18 and 19. As shown, this mechanismincludes an adjustable displacement hydraulic piston 270 operating in acylinder 272 suitably mounted on the cradle housing 30 of the roughingmachine and preferably directly in the corresponding position occupiedby the helical motion cam and follower (not shown) ofa finishingmachine. The piston 270 acts directly on a roller 274 carried by a crank276 drivingly connected to an eccentric member 278, arranged for drivingor moving the cradle in a direction along its axis, as is disclosed morefully in the copending application of Hunkeler et al., Improved CradleAssembly For Gear Cutting Machines and Means For Moving Cradle Axially."When pressure is admitted to the cylinder 272, as through port 280, thepiston 270 will be moved downwardly to rotate the crank 276 andeccentric 278 counterclockwise, as viewed in FIG. 18, and thiscounterclockwise rotation of the crank will effect an abrupt withdrawalof the cradle axially in the cradle housing, and against pressureexerted on the cradle to keep it in an advanced position, as will beunderstood from the copending application just referred to. The amountof withdrawal of the cradle will be controlled by the adjustable gap 282which limits the downward movement of the piston against the top of thecylinder, as will be evident. A suitable adjusting knob 284 may beprovided at the top of the piston 270, for example, in threadedconnection therewith, as shown, so that rotation of the knob will effectan increase or decrease in the size of the gap 282 to increase ordecrease the stroke of the piston, thereby increasing or decreasing theamount of axial movement of the cradle caused thereby. A pin 286 isshown as arranged in the lower end ofthe cylinder 272 and extending intoa vertical slot in the piston so as to permit rotary adjusting movementsof the knob 284 while the piston is held stationary rotationallythereby.

For the return setover, pressure will be exhausted fromthe cylinder 272and the crank will be rotated clockwise, as viewed in FIG. 18 (beingactuated by pressure in the cradle as disclosed in the last referred tocopending application) to move the piston 270 upwardly until the cradlereturns or advances axially inwardly to the position controlled by apositive stop (not shown) therefor.

HYPOID OFFSET SETOVER The illustrative embodiment of fro hypoid offsetmechanism 288 is shown in FIGS. 16 and 17. It is contemplated that thismechanism will operate so as to provide for both a substantial offset ofthe cradle axis horizontally and at right angles to the work axis (alsoto the normal cradle axis), for example, during initial setup, and alesser but abrupt setover to and fro from this basic position duringoperation. It is further contemplated that these adjusting movements ofthe cradle be accomplished by movement of the entire cradle housing 30with respect to the machine frame 26. As best seen in FIG. 16, thismechanism includes an internally threaded element 290 mounted in fixedor stationary position in a bracket 292 suitably fixed to the machineframe. A threaded stem member 294 is screwed through the nutlike element290 and is adapted to be threaded in either direction within thiselement. As shown, the left end of the stern 294 is provided with acollar 296 suitably journaled and held axially in a recess within apiston member 298, as shown. This piston is arranged for slidingmovement within the cylinder 300 which is suitably attached in fixedposition to the cradle housing 30.

Relative movements of the piston 298 and cylinder 300 are provided bythe hypoid offset setover. In the action of this setover the piston willremain stationary relative to the machine frame, and with pressurereversals, for example, admitting oil under pressure alternately to theleft and right cylinder ends 302 and 304 through suitable passageways,as shown, the cylinder carrying with it the entire cradle housing willbe moved alternately to the left until it strikes the positive stop 306,and to the right until it strikes positive stop 308, the piston head.Suitable means may be provided by adjusting the gap or distance betweenthese stops 306, 308, as shown. Such means includes an internallythreaded calibrated adjusting nut 310 calibrated on a loose sleeve 311and adjustably screwed onto a threaded member 312 fastened to the piston298 in a locked position therewith, as shown. When adjustment of nut 310is made, the locking screw 314 will be tightened, fixing the nut in thisadjusted position relative to the threaded member 312. A pointer P maybe provided, as shown.

For making the much larger, basic hypoid offset setting of the cradle,pressure can be admitted to one side of the cylinder, as at theright-hand end thereof, as viewed in FIG. 16 and the screw 294 will bemanually rotated by suitable means so as to move axially in thestationary bracket 292 and carry with it axially the entire assemblyincluding the piston 298, cylinder 300 and cradle housing 30.

A differential calibrated dial assembly 316 is shown as arranged on theleft end of the threaded member 294, and includes a dial 318 adjustablyconnected to the member 294, as by setscrew contact with a sleeve 295keyed to the member 294, as indicated at 297. The dial assembly includesa pointer 320 carried by member 312. While making the larger, basichypoid offset setting, the dial 318 will rotate with the threaded member294 and the pointer and member 312 will not rotate, as will be evident.Suitable means may be provided for preventing rotation of the piston 298as, for example, a pin

1. In the method of making bevel gears having tapering tooth slots usinga tool mounted in a movable toolholder and a workholder mounting aworkpiece, with means providing for generating rolls between tool andworkpiece, a preliminary roughing operation comprising the steps of:effecting a plunge feed between the tool and the workpiece to provide apartial tooth slot of less than the depth of the final, desired, roughedtooth slot; providing a cutting, generating, forward roll between thetool and workpiece; and then providing a return roll between the tooland workpiece, said forward and return rolls each terminating short ofthe roll out points of generation at both the toe and heel of theworkpieCe.
 2. The method defined in claim 1 wherein there is no cuttingaction on the return roll, and wherein there is no additional depth feedbetween the tool and the workpiece during the forward generating roll.3. The method defined in claim 1 wherein the workpiece is a bevel piniongear blank and wherein the plunge feed occurs in the region of the heelof the workpiece.
 4. In the method of making bevel gears of taperingtooth slots wherein gear blanks are first rough cut and wherein thereare provided two rough cutting stations, each including a tool mountedin a movable toolholder and a workholder mounting a workpiece and meansproviding for generating rolls between tool and workpiece, andimprovement which comprises: subjecting a workpiece to a first roughingoperation at the first of said stations wherein tooth slots are roughcut in the workpiece only to partial depth; transferring the workpieceto the second of said roughing stations; and completing the roughingoperation at said second station, by a further rough cut wherein thetooth slots are shaped more substantially to the desired, finishedconfiguration thereof and including removal of material from the bottomof the tooth slots.
 5. The method defined in claim 4 wherein said firstroughing operation includes: effecting a plunge feed between the tooland the workpiece at the beginning of the cutting cycle for a tooth slotand terminating the plunge feed at a depth less than the depth of thefinal, desired, roughed tooth slot.
 6. The method defined in claim 5wherein said first roughing operation further includes a cutting,generating, forward roll between tool and workpiece at the end of saidplunge feed while still only cutting the tooth slot to partial depth,and then effecting a return roll between tool and workpiece, saidforward and return rolls each terminating short of the roll out pointsof generation at both the toe and heel of the workpiece.
 7. The methoddefined in claim 6 wherein there is no cutting action on the returnroll.
 8. The method defined in claim 6 wherein there are no setovers atthe end of the cutting roll.
 9. The method defined in claim 4 whereinthe second roughing operation includes a first generating roll, and areturn generating roll, with cutting being performed during both rolls,and with the ratio of roll between tool and workpiece different for eachof said rolls.
 10. The method defined in claim 9 and further whereincutting operations are going on simultaneously on two differentworkpieces, one at each of said stations.
 11. The method defined inclaim 10 and further including feeding workpieces in the form of gearblanks to a first region adjacent and first roughing station,automatically and periodically feeding gear blanks from said region tosaid first cutting station and then to said second cutting station andthen to a discharge region, so as to provide a single production line.12. The method defined in claim 11 wherein said discharge regioncoincides with said first region and further wherein the workpiece isautomatically positioned in the workholder in said second station in acertain, predetermined relation to the tool at that station forautomatic stock division during the second roughing operation.
 13. Themethod defined in claim 6 wherein the second roughing operation includesa first generating roll, and a return generating roll, with cuttingbeing performed during both rolls, and with the ratio of roll betweentool and workpiece different for each of said rolls.
 14. The methoddefined in claim 13 and further wherein cutting operations are going onsimultaneously on two different workpieces, one at each of saidstations.
 15. The method defined in claim 14 and further includingfeeding workpieces in the form of gear blanks to a first region adjacentsaid first roughing station, automatically and periodically feeding gearblanks from said region to said first cutting station and then to saidsecond cutting station and then to a dIscharge region, so as to providea single production line.
 16. The method defined in claim 15 whereinsaid discharge region coincides with said first region and furtherwherein the workpiece is automatically positioned in the workholder insaid second station in a certain, predetermined relation to the tool atthat station for automatic stock division during the second roughingoperation.
 17. In the method of making bevel gears having tapering toothslots using a tool mounted in a movable toolholder and a workholdermounting a workpiece, with means providing for generating rolls betweentool and workpiece, a preliminary roughing operation for forming roughedtooth slots in sequence and comprising the steps of: effecting a plungefeed between the tool and the workpiece to provide a partial tooth slotof less than the depth of the final, desired, roughed tooth slot;providing a cutting, generating forward roll between the tool andworkpiece whereby the preliminary, roughed tooth slot is produced; thenproviding a return roll between tool and workpiece during which nocutting takes place and indexing the workpiece for the next tooth slotto be cut therein; providing a partial forward generating roll withoutcutting prior to forming the next tooth slot; effecting a plunge feedbetween the tool and the workpiece to provide a partial tooth slot ofless than the final, desired depth for the next roughed tooth slot; andthen providing a cutting forward generating roll between tool andworkpiece whereby the next preliminary, roughed tooth slot is produced,said forward and return rolls each terminating short of the roll outpoints of generation at both the toe and heel of the workpiece.
 18. Amethod of rough cutting bevel gears in two successive operations at twosuccessive stations wherein each station includes a tool mounted in amovable toolholder and a workholder mounting a workpiece, with meansproviding for generating rolls between tool and workpiece, the first ofsaid operations comprising a plunge feed between the tool and theworkpiece without a generating roll and only to partial depth of thefinal roughed tooth slot desired and thereafter providing a cutting,generating roll at the same partial depth to produce a preliminary,roughed tooth slot, and thereafter providing for relative withdrawalbetween the tool and the workpiece and rapid return roll between thetool and the workpiece, and then indexing the workpiece for the nexttooth slot to be roughed, and the second of said operations comprisingcutting the preliminary roughed tooth slots to the depth desired for thefinal roughed tooth slot.
 19. The method defined in claim 18 whereinsaid second operation includes a first generating roll, and a secondgenerating roll, with cutting being performed during both rolls and withthe ratio of roll between tool and workpiece different for each of saidrolls.
 20. The method defined in claim 1 wherein the forward and returngenerating rolls each terminate a relatively substantial distance shortof the roll out points of generation at both the toe and heel of theworkpiece.
 21. In the method of making bevel gears having tapering toothslots using a tool mounted in a movable toolholder and a workholdermounting a workpiece, with means providing for generating rolls betweentool and workpiece, rough cutting the tooth slots in the workpiece intwo separate stages wherein the first stage comprises the steps of:effecting a plunge feed between the tool and the workpiece to provide apartial tooth slot of less than the depth of the final, desired, roughedtooth slot; providing a cutting, generating, forward roll between thetool and workpiece; and then providing a return roll between the tooland workpiece, said forward and return rolls each terminating short ofthe roll out points of generation at both the toe and heel of theworkpiece.